1. Field of the Invention
The present invention relates to a method for development-processing a presensitized plate for use in making a lithographic printing plate (hereinafter optionally referred to as "PS plate(s)") and more particularly to a method for maintaining a constant activity of a developer during development-processing by supplementing a replenisher for developer.
2. Description of the Prior Art
It has been known to recover a developer deteriorated by developing a large number of PS plates through the addition of a replenisher therefor.
For instance, Japanese Patent Un-examined Publication (hereinafter referred to as "J.P. KOKAI") No. 56-115039 (British Pat. No. 2,046,931) discloses such a technique which permits a long-term running development by replenishment for compensating the deterioration of the developer by carbon dioxide in the air and by replenishment for compensating the deterioration of the developer by development of PS plates; J.P. KOKAI No. 58-95349 (U.S. Pat. No. 4,537,496) discloses a technique which comprises disposing a sensor in the middle of a developing zone of an automatic developing machine, monitoring the degree of light-sensitive compositions dissolved out from the processed PS plates, and automatically operating a device for supplementing a replenisher for developer when the degree of light-sensitive composition dissolved out, which is detected by the sensor, is reduced to a desired level so that a desired amount of the replenisher for developer is supplemented to the automatic developing machine; and J.P. KOKAI No. 61-61164 discloses a technique comprising determining the electric conductivity of a developer and operating an apparatus for supplementing a replenisher for developer when the level of the electric conductivity thereof is lowered to a predetermined level as the amount of the materials processed is increased so that a desired amount of the replenisher for developer is supplemented to a developing bath.
However, in the technique disclosed in J.P. KOKAI No. 56-115039 (British Pat. No. 2,046,931), a constant amount of the replenisher is always supplemented if the PS plates processed have a constant length irrespective of the change in the width and image areas thereof. Moreover, a constant amount of replenisher for developer is also supplemented in the case of replenishment for compensating the deterioration of the developer by carbon dioxide in the air. However, the optimum amount of the replenisher is greatly influenced by the amount of the developer initially charged into an automatic developing machine and the concentration of carbon dioxide present in the air.
As explained above in detail, the aforementioned conventional techniques suffer from drawbacks such that the precise recovery of the deteriorated developer cannot be attained unless the amount of the replenisher is changed at each time while taking, into consideration, various factors such as the width of PS plates, image areas thereof, the amount of the developer initially charged into the automatic developing machine and the concentration of carbon dioxide in the air.
Under such circumstances, many attempts have been directed to the development of methods which makes it possible to eliminate the foregoing drawbacks. For instance, J.P. KOKAI No. 58-95349 (U.S. Pat. No. 4,537,496) cited above discloses a technique which gives lithographic printing plates having high stability and high quality. However, in this method, it is required to coincide nonimage areas of the PS plates with the position on which a sensor is disposed and further it is difficult to incorporate related devices such as an autofeeder into the automatic developing machine. In addition, J.P. KOKAI No. 61-61164 discloses a technique in which supplementation of the replenisher for developer is effected on the basis of the following empirical exponential function of the number of replenishment (X): EQU Z=6.09.times.X.sup.p
wherein Z is the lower limit of electric conductivity of a developer at which the supplementation of the replenisher is to be carried out; and p is a constant which is determined in accordance with the kind of light-sensitive layer of the PS plate to be processed. However, the electric conductivity of a developer or hence the lower limit thereof is influenced by various factors such as the kind of the light-sensitive layer processed (i.e., the foregoing factor p), the volume of tanks for the automatic developing machine, the charged amount of the developer, the amount of a replenisher supplemented, the concentration of CO.sub.2 and evaporation of water and, therefore, the lower limit (Z) cannot be correctly determined simply by the number of replenishment (X). Therefore, a stable supplementation cannot be achieved by such a technique disclosed therein.